1. Technical Field
The present invention relates to a reclose or zipper seal jaw design for use in a sealing carriage of a vertical form and fill packaging machine, and, in particular, to a quick-change, reclosable zipper seal jaw module and standard or xe2x80x9creturnxe2x80x9d module that can accommodate variable bag sizes. The modules are self-aligning, easily installed on existing bridge assembly hardware, and incorporate several safety enhancements.
2. Description of Related Art
Vertical form, fill, and seal packaging machines are commonly used in the snack food industry for forming, filling, and sealing bags of chips and other like products. Such packaging machines take a packaging film, such as polypropylene, from a sheet roll of said film, and forms the film into a vertical tube around a product delivery cylinder. The vertical tube is vertically sealed along its length to form a back seal. The machine applies a pair of heat-sealing jaws or facings against the tube to form a transverse seal. This transverse seal acts as the top seal on the bag below and the bottom seal on the package being filled and formed above. After the seal has been formed, the film tube is pushed downward to draw out another package length. The package below the transverse seal is separated by cutting across the sealed area.
Before each transverse seal is formed by the sealing jaws, the product to be packaged is dropped through the product delivery cylinder and formed tube and is held within the tube above the bottom transverse seal. Prior to forming the upper transverse seal, the sealing jaws are brought together in two steps. First, a pair of stripping plates or bars are brought into contact with the film in order to flatten the tube and strip product out of the area to be sealed. Second, the final closing movement of the jaws is performed, thereby forming the transverse seal.
The bag sealing functions of a vertical form, fill, and seal machine are best described with reference to FIGS. 1a and 1b. FIG. 1a shows a sealing carriage on a prior art form, fill, and seal packaging machine. FIG. 1b is a cross-section of a prior art facing assembly installed in said carriage. Opposed transverse seal jaw facings 102, 104 (hereinafter referred to by Applicants as xe2x80x9cjaw facingsxe2x80x9d) are shown attached to opposed bridge assemblies 106, 108. Behind each jaw facing 102, 104 is a heat probe 128, 130 capable of heating the exposed surface of the jaw facings up to 405xc2x0 F. during operation. Placed between the jaw facings 102, 104 and their respective bridge assemblies 106, 108 is a heat separator 136, 138. The heat separators 136, 138 provide a thermal barrier between the jaw facings 102, 104 and the bridge assembly 106, 108 in order to minimize heat transfer to the bridge assembly 106, 108 and other components attached thereto. A thermocouple or thermoster 132, 134 is placed between the heat separator 136, 138 and the heat probe 128, 130 in order to monitor the jaw facing 102, 104 temperature. As previously described, a transverse seal is formed when a tube of film placed between the jaw facings 102, 104 is flattened as the jaw facings 102, 104 are brought in close proximity to each other. This is accomplished by both bridge assemblies 106, 108 traversing towards each other while riding on two stationary rods 110, 112.
Also shown attached to the bridge assemblies 106, 108 are a pair of opposed crumb plates 114, 116. When the bridge assemblies 106, 108 are brought together, the crumb plates 114, 116 slightly overlap, thereby forming a temporary xe2x80x9cSxe2x80x9d shaped constriction in the flattened film tube. This xe2x80x9cSxe2x80x9d shaped constriction provides a means for keeping product out of the transverse seal area while the tube of film above the constriction is filled with product. Two stripper bars 118, 120 are also shown attached to the bridge assemblies 106, 108. The stripper bars 118, 120 are typically spring loaded and provide the stripping function previously described.
Both of the jaw facings 102, 104 are constructed with a central channel 141, 143 to accommodate a knife or cutting tool 122. This knife 122 is recessed within the channel 141 of one of the jaw facings 102 and held in place by two knife brackets 124, 126 attached to the bridge assemblies 106, 108. After the transverse seal has been formed on the flattened film tube, the knife brackets 124, 126 are rotated slightly, thereby exposing the knife 122 to the transverse seal. This action cuts the transverse seal, thereby completing the process of forming, filling, and sealing a single package.
The prior art carriage described above is designed such that the jaw facings 102, 104 can be removed in order to install jaw facings 102, 104 that provide for different vertical widths of the resultant transverse seals. The facing assembly shown in FIG. 1b is aligned at the factory, and removal from the sealing carriage by the operator of more than the jaw facings 102, 104, crumb plates 114, 116, and stripper bars 118, 120 is not recommended. Such design is also not easily adapted to the formation of a zipper seal along with the standard transverse seal. In fact, as will be explained below, a form, fill, and seal packaging system must be substantially modified when it is used to install a zipper seal at the top of the package.
A zipper seal is a resealable barrier that can be installed on the top end of a bag either immediately below or above the upper transverse seal. After the consumer breaks the upper transverse seal to gain access to the product within the package, the zipper seal can be reclosed, thereby keeping the product fresh. Such package is referred to as a xe2x80x9creclosexe2x80x9d bag. Consequently, the terms xe2x80x9czipper seal modulexe2x80x9d and xe2x80x9creclose module,xe2x80x9d and many other descriptive terms using as adjectives the words xe2x80x9czipperxe2x80x9d or xe2x80x9creclose,xe2x80x9d are used herein by Applicants interchangeably.
FIGS. 2a and 2b show one embodiment of a reclose food package 281 incorporating a zipper seal 283. FIG. 2a is a perspective view of a flexible, plastic package or bag 281 used to contain potato chips, tortilla chips, and the like. FIG. 2b is a cross-section of the top of said bag 281. The food package 281 shown is typical in that it has an upper transverse seal 285 and a lower transverse seal 287. However, this bag also uniquely incorporates a zipper or reclose seal 283 immediately below the upper transverse seal 285. The zipper seal 283 is made up of a male engagement member 291 and a female engagement member 289.
For the embodiment illustrated, the package 281 is opened for the first time by pulling on the exterior walls of the package 281 below the zipper seal 283. The two opposed members 289, 291 separate, thereby opening the zipper seal 283. Stress can then be exerted on the upper transverse seal 285 until it opens. Once this occurs, the package 281 is fully opened and the product, such as tortilla chips 293, may be consumed. The package 281 can then be resealed by applying pressure to the exterior of the package 281 along the zipper seal 283, thereby forcing the male engagement member 291 back into the female engagement member 289. This novel reclose bag design is described in detail in U.S. patent application Ser. No. 09/079,382 filed on May 15, 1998 now U.S. Pat. No. 5,972,386.
When making the reclose bag 281 illustrated, the opposed members 289, 291 (of the zipper seal 283) must be heat sealed to the inside surface of the food package 281. Further, these opposed members 289, 291 must be heat-sealed together at each end 295, 297. This is accomplished by applying a heat and pressure sealing device to an outer areas of the zipper seal 283.
The film that enters a form and fill machine to form the reclose package 281 shown in FIG. 2a is typically a continuous sheet with graphics presented on one side. The side of the sheet on which the graphics are presented will ultimately comprise the outside of the package 281. The unprinted side of the sheet will ultimately comprise the inside of the package 281. Prior to entering the form and fill machine, zipper seals 283 must be attached to the inside film surface by securing one of the opposed members 289, 291 on the inside surface of the film with the zipper seal 283 in the closed configuration position. The zipper seal 283 thus secured should be oriented such that when the upper transverse seal 285 is formed on the package 281, the zipper seal 283 is located in its proper position below and parallel to the upper transverse seal 285. This will allow for the formation of both the transverse seal 285 and the permanent attachment of the zipper seal 283 to the inside of the package 281. The simultaneous formation of the transverse seal 285 and the installation of the zipper seal 283 can be accomplished with an extensively modified prior art sealing carriage, in part by installing a second set of facings for sealing the zipper seal into the package along with the existing set of facings. As will be described, such adaptation of an existing form and fill sealing carriage makes for a number of technical difficulties and unsatisfactory results.
FIGS. 3a and 3b illustrate one prior art embodiment known to Applicants of a modification of a sealing carriage to accommodate the formation of a reclose bag. FIG. 3a is a perspective view of a modified sealing carriage, while FIG. 3b is a cross-section of the modified facing assembly. By comparing FIGS. 3a and 3b with FIGS. 1a and 1b, it is evident that a second set of opposed facings 340, 342 have been installed below the first opposed set of facings 302, 304. The second set of opposed facings 340, 342 are the means for sealing the zipper below the transverse seal on the reclose bag. Consequently, they are known as zipper seal jaw facings 340, 342 and referred to herein by Applicants as xe2x80x9czipper seal facings.xe2x80x9d The stripper bars 318, 320 are now attached below the zipper seal facings 340, 342. Each of the zipper seal facings 340, 342 must also have a respective heat probe 344, 346 and thermosters 348, 350.
Prior art modifications to the sealing carriage of a form and fill packaging system to accommodate the manufacture of reclose bags are not easily installed, have exhibited poor performance characteristics, raise several safety concerns, and are only suitable for one package size and zipper configuration. Consequently, the modification shown in FIGS. 3a and 3b is not a desirable fix. As will be explained, the purchase of a dedicated form and fill machine only capable of constructing reclose bags is also not an acceptable alternative.
By way of background, most chip packaging facilities have on-site one to several (and perhaps as many as seven or eight) vertical form, fill, and seal packaging machines. A single packaging facility might be required in any given week to package several different product lines in numerous different bag sizes for each product line by using the same form and fill packaging machines. Each form and fill packaging machine is quite expensive, for example, in the range of $50,000 to $150,000, and represents a large capital investment. Consequently, it is critical to the economic efficiency of the packaging facility that each form and fill machine be capable of being quickly adapted to handle a variety of bag widths and lengths. This is easily done with the prior art vertical form, fill, and seal machine discussed herein for standard (non-reclose) bags. The facings 102, 104 (shown in FIG. 1a) can accommodate any required bag width up to the total width of the facings 102, 104. The bag length is easily adjusted by changing the amount of film travel below the facings 102, 104. However, converting a prior art vertical form, fill, and seal machine from the configuration shown in FIGS. 1a and 1b to the configuration shown in FIGS. 3a and 3b requires extensive modifications to the machine to allow for additional attaching points, electrical connections, controls, and to accommodate additional stripper travel. Once these modifications are made, it typically takes several hours to install the additional set of facings and accompanying heat probes, stripper plates, and other required items. It then takes an additional several hours to reconvert the assembly back to a standard transverse seal configuration.
It is expected that a typical packaging facility will only need to dedicate a small portion of the packaging assets to the formation of reclose bags incorporating zipper seals. Consequently, a permanent changeover to a reclose bag configuration or the use of a specifically built reclose bag machine would result in such packaging machine sitting idle for long periods of time. The ability to quickly change over from a standard transverse seal configuration to a reclose configuration is, therefore, a major consideration. The present down-time involved in changing from one configuration back to the other, which is in excess of several hours, adds considerably to the labor costs in running reclose bags and reduces the overall packaging capacity of any single packaging facility.
Along the same lines, prior art reclose designs allow for the production of only one bag width for any given set of zipper seal facings 340, 342. This is due to the fact that the zipper seal facings 340, 342 have a rectangular shaped recess in order to accommodate the zipper seal while at the same time sealing the zipper seal at each end and around its edges to the inside of the bag. If a change in bag size is required for a reclose bag, the zipper seal facings 340, 342 must be removed from the reclose assembly and replaced with a new zipper seal facing 340, 342 to accommodate the new bag""s width. This again takes two to four hours to accomplish, thereby requiring additional man hours and reducing the efficiency of the packaging facility. The zipper seal facings 340, 342 are also expensive items, presently costing approximately $7,500.00 per each set of facings 340, 342. Capital investment must therefore be made for every conceivable bag width so that a specific sized zipper seal facing 340, 342 can be on hand whenever a corresponding bag width needs to be run on the form and fill machine in the reclose configuration.
The need to replace components on the modified carriage and facing assemblies shown in FIGS. 3a and 3b increases the safety hazards involved in such change over operation. In order to remove or install the zipper facings 340, 342 and related components, it is necessary to bring the carriage to the open position. An inadvertent activation of the closing feature of the carriage while an operator is attempting to remove or install a component could result in serious injury. Further, during operation the various facings 302, 304, 340, 342 are heated to 350xc2x0 F. In order to remove the facings 302, 304, 340, 342 after operation, they must either be allowed to cool or careful attention must be paid to insure that the operator is not burned by the facings 302, 304, 340, 342 or accompanying heat probes 328, 330, 344, 346. The cutting knife 122 is also extremely sharp and must be carefully removed.
The placement of the zipper seal facing 340, 342 below the standard jaw facing 302, 304 also introduces several problems. It can be seen from FIGS. 2b and 3b that the area that is required to be stripped of product prior to applying both a standard transverse seal and a reclose seal is approximately doubled in length compared to the area that requires stripping when only a transverse seal is formed. More importantly, with the zipper seal 283 located below the transverse seal 285, the zipper seal 283b is closest to the product and will always have to be stripped even if portions of the transverse seal 285 do not require stripping. This is problematic in that the zipper seal 283 is significantly thicker than the transverse seal 285. Effective stripping widths for a transverse seal 285 are on the order of 0.030 inches, while effective stripping widths for a zipper seal 283 are on the order of 0.125 inches. Consequently, stripping efficiency of the transverse seal area is lost because the strippers must be set to accommodate the thicker zipper seal 283 located below. Further, the chassis or frame of the form and fill machine must be modified to allow space for stripping in light of the addition of components below the existing facings and accompanying stripper bars. The alternative is to limit the amount of stripping travel, which in turn limits the ability to remove product from the sealing areas.
It is also evident that the zipper seal facings 340, 342, unlike the jaw facings 302, 304, are not centered along the axis of the closing force acting on the carriage. FIG. 3b shows two force vectors F indicating that the force exerted on the assembly is centered along the axis of travel of bridge assemblies 306, 308 along the stationary rods 310, 312. These force vectors typically produce a pressure of 1000 to 1200 psi along the facings 302, 304 during seal formation. However, the rigidity of the facing assembly shown in FIG. 3b is not sufficient to equally distribute this pressure because of the cantilevered location of the zipper seal facings 340, 342 away from the centerline of the supporting bridge assemblies 306, 308. The zipper seal facings 340, 342 act as lever arms rotating away from the force F centered on the bridge assemblies 306, 308. Unless this phenomena is counteracted, sufficient pressure cannot be applied on the zipper seal to adequately and uniformly attach it to the inside of the bag. A prior art fix to this problem is to install springs (not shown) behind the zipper seal facings 340, 342 in order to counteract the rotating effect. This fix has been demonstrated to reduce the overall pressure applied by the carriage assembly on the bag film. To counteract this loss of pressure, the heat or the dwell time must be increased, or both. Increasing the dwell time reduces the productivity of the bag maker, while heat can only be increased to a certain level before other adverse consequences are experienced.
Consequently, a need exists for a modular zipper seal jaw unit that can be easily removed from or installed on a prior art form and fill packaging machine sealing carriage, thereby quickly modifying the sealing carriage for a reclose configuration. This zipper seal jaw module should incorporate safety features to keep the operator away from heat sources and should physically lock in the closed position in order to avoid inadvertent closure of the device on the operator""s hands during removal or installation. Ideally, the module should be self-aligning and quickly installable with a minimal number of tools. The module design should allow for a uniform application of pressure during the sealing mode between the jaw facings and the zipper seal facings. Further, the orientation of the module should allow for no interference with the form and fill machine chassis during stripping and promote increased stripping efficiency. A single module should be easily convertible to handle any width reclose bag without the need to stock and replace various sizes of zipper facings. The invention should also incorporate a standard return module that can be quickly and easily substituted for the reclose module to return the form and fill package machine to standard transverse seal operation.
The proposed invention comprises a quick-change zipper seal jaw module and accompanying return module that are self-aligning and easily installed in less than fifteen minutes with a single standard tool. The zipper seal module uses two rigid support members to support an opposed pair of zipper seal facings and an opposed pair of jaw facings. The support members can also support crumb plates and stripper bars, as needed. Each support member is easily attached to an existing bridge assembly with one or more bolts. Each support member also has at least one threaded receiver for receiving a bolt from an aligning tool. This aligning tool holds the opposed facings together in an aligned position when the module is being installed, removed, or while in storage. The heating requirements of the module are completely self-contained and connected to electrical quick-connect plugs which mate with quick-connect outlets installed on the chassis of the form and fill machine.
The zipper facings are located above the jaw facings in one embodiment of the invention. This requires that the package film be run upside-down, but also increases stripping efficiency, since the thicker zipper seal is located further from the product level in the bag during sealing. Further, the zipper seal facings and jaw facings are oriented such that the pressure applied on the module by the bridge assemblies during a sealing step is generally distributed equally about all facing contact surfaces. A knife adapter is provided to move the location of the knife to the repositioned jaw facings.
In one embodiment of the invention, the zipper seal facing is constructed of a slotted channel that allows for the installation of end inserts. This allows for the same zipper facing to be used to make varying widths of reclose bags by merely changing the size of the end inserts or moving the inserts relative to each other within the slotted channel.
The invention also provides for a xe2x80x9creturnxe2x80x9d module which returns the vertical form, fill, and seal machine to a standard transverse seal configuration using the same mounting hardware as used with the reclose or zipper seal module. The return module is also self-aligning by use of an alignment handle.
The invention is a great improvement over the prior art for a number of reasons. The time involved in changing a form and fill machine from a standard transverse seal configuration to a reclose configuration has been reduced from several hours to less than 15 minutes. A similar time saving is involved when adjusting the zipper seal facing of the invention for varying bag widths since the zipper seal facing need not be removed. This feature also saves a considerable amount of capital investment, since changing a reclose bag width does not require the use of a different, and expensive, size jaw facing.
The use of an aligning handle with both the reclose module and return module greatly increases safety during change-over operations and when required maintenance must be performed. Since the module is completely self-contained, maintenance on heat probes, thermosters, and other module components can be done off-line and away from the potential crushing hazards associated with working on sealing carriage components while the sealing carriage is in the open position. Changing facings can also be done off-line. The modular installation and removal using the aligning handle is done with the sealing carriage in the closed position, thereby keeping an operator away from hot components immediately after operation and reducing the chance of the facings inadvertently closing on an operator""s hand.
The invention performs the sealing function more efficiently than prior art designs and increases stripping efficiency due to the reversed and centered relative orientation of the jaw facings and zipper seal facings. Normal dwell times and temperatures can be used while still producing uniform and acceptable transverse seals and zipper seals. The orientation of the facings centered on the bridge assembly also adds minimally to the vertical space required below the bridge assemblies to accommodate stripping travel. Therefore, the modules do not interfere with an existing form and fill machine chassis during the stripping phase of package formation.
The above as well as additional features and advantages of the present invention will become apparent in the following written detailed description.